Prepare mushrooms: wash, put to boil in salted water until ready (15 minutes after boiling).
While the mushrooms are cooking, marinate the onions. For this onion thinly cut chetvertfinalny, to shift into a deep bowl, sprinkle with sugar (about a tablespoon no slides), salt (a teaspoon without slides), mix well and pour over the vinegar (3 tablespoons). Leave on for 15 minutes.
Boiled mushrooms cool and cut into thin plates.
Seaweed cut so it won't be long strips (and then the mixing products are unevenly distributed).
To add seaweed boiled mushrooms, onions, finely chopped walnuts. All thoroughly mix.